You might want to incubate the inoculated eggs for 24-36 hours as is commonly practiced for wild type H5 viruses.  You might just want to collect at 12, 24, 36 hours post inoculation.  Check for embryo viability prior to chilling the eggs.  Hope this helps.

Low yield after egg inoculation can be due to a high virulence leading to a quick death of the chick embryo (harvesting must be, in this case, made earlier as suggested in a previous answer) but can also be the result of a poor viral growth which is not unlikely in your case since your viral strain is mouse adapted. I would thus suggest to test several times for collection before and after 48h pi (up to 72h). In addition, the optimal incubation temperature is likely, for your mouse adapted variant, to be lower than for typical avian strains. 

Hi Ahmed, i totally agree with Mutien and Trushar but another advice is to try to activate the strain firstly on mice before egg adaptation if the strain stored for long period. if there is no increase in the titre, you will try three successive passages on egg as virus is mouse adapted and you will obtain high titre.

regards 

I agree with Trushar Jeevan . Try & check at different period of post inculation incubation for virus after chilling over night.

Also I advice alter the incubation temperature if done at 37 o C, try 35 oC or Vice versa